This invention relates to logging plugs for use in oil, gas and other wells.
To ascertain parameters of well operations such as pressure, temperature and flow rate one or more logging tools are run down the well on logging tool suspension means, for example an electrical logging cable or slick line. As many of these parameters in the perforation zone must be measured while the pressure there is different from that obtaining in the upper part of the well down which the logging tool is run, it is necessary for the suspension means to be passed through a logging plug which maintains a good, but not perfect, seal with the suspension means, and which is itself sealable within a nipple profile incorporated in production tubing, by-pass tubing or the well casing.
Considerations arising from typical employments of a conventional logging plug have been discussed in our co-pending Application PCT/GB89/00799 (WO 90/00667) which corresponds to U.S. Pat. No. 5,099,919, which is incorporated herein by reference.
It was an aim of the earlier invention to provide a logging plug which allowed the pressures obtaining above and below the plug to be equalized and thus allow withdrawal of the plug and logging tools.
According to the earlier invention there was provided a logging plug for suspension down a well, comprising a hollow body provided with sealing means by which it could be sealed within a nipple profile included in a tubing string, the body also providing or receiving means to allow suspension means to be passed therethrough while maintaining a substantial seal, and an equalizing member through which the suspension means could freely pass and which was arranged for sliding movement within said body between a first position in which communication past said sealing means was prevented and a second position in which communication past the sealing means was allowed.
Preferably the equalizing member had at least one port communicating with an axial bore through which the suspension means passed and which in the first position was closed by a sleeve forming part of the hollow body, and in the second position communicated with one or more ports formed through the wall of the hollow body.
Preferably again, the equalizing member was located at the lower end of the logging tool so that it could be displaced from the first to the second position by the upward impact of a logging hammer or of a logging tool attached to the suspension means.
A disadvantage of known logging plugs, and indeed the plug according to our earlier invention, is that the plug may have to be seated in position by the weight of a logging hammer secured to the suspension means above the plug. Securing the hammer is a time-consuming operation involving the use of expensive pressure lock apparatus.